Prior to the development of the present invention, as is generally well known in the art, a rotary door operator is mainly used in the inter-city bus coaches. These rotary operators are available in two distinct types, commonly referred to as zero-lead and lift-and-lock. Either door operator type can be adapted for use with pneumatic or hydraulic fluids.
The rotary operator of the zero-lead type converts piston motion of a piston-power cylinder unit into a rotary motion by means of roller pairs engaging oblique slots with an axial direction at their ends. One of the cylinders within the piston-power cylinder unit is connected to the power output shaft that, in turn, is connected to a door of the vehicle. During the door closing cycle, the power shaft moves upwardly in the vertical direction. When the door reaches a closed position, the roller pairs disposed at the end of the axial portions provide rudimentary locking of the door providing that the piston-power cylinder unit is charged with fluid and that no leakage occurs.
The rotary door operator of the lift-and-lock type comprises a double acting drive cylinder driving an output shaft coupled to the door post. The output shaft has a splined shaft member connected to the cylinder through a helical ball cage in order to provide a rotary motion and engageable with the door post carrying the door. The output shaft also has an antirotational shaft member enabling vertical movement of the output shaft to lock and unlock the door. When the door reaches the closed position, the rotary door operator lifts the door post and, subsequently, the door connected to the door post by approximately 10 mm, enabling door mounted wedges to engage mating wedges mounted adjacent a portal aperture of the transit vehicle. In the opening direction, the output shaft first moves in a downward direction disengaging the wedges and enabling rotation of the door post.
To close the transit vehicle door, the drive cylinder is charged with fluid pressure through the first orifice. The rate at which the door closes depends solely on the rate at which the cylinder is charged with fluid. The splined shaft member connected with a drive cylinder piston moves linearly in the upward direction while engaging an antirotational shaft member. Such upward motion of the output shaft causes rotation of the post in the first direction and, more particularly, causes the closing motion of the door.
To open the transit vehicle doors, the drive cylinder is charged with fluid pressure through the second orifice. The rate at which the door opens depends solely on the rate at which the cylinder is charged with air. The output shaft moves linearly in the downward direction and causes rotation of the splined shaft in the second direction to open the door.
Such lift-and-lock feature is the mechanism disposed within the door operator preventing the un-locking of the door. When such door contacts door jambs of the door portal aperture, the mounting linkage attached to the door at one end and attached to such door operator at the distal end stops rotating. Since the cylinder has not reached the end of the stroke, the output shaft continues to move upward lifting such door and enabling door locking wedges to substantially engage mating locking wedges disposed adjacent the portal aperture.
One of the main disadvantages of these designs is that loss of fluid pressure will cause downward movement of the door, thus disengaging such mating wedges in lift-and-lock applications or simply unlock the door in zero-lead applications and, more particularly, loss of fluid pressure will create a hazardous condition due to an unlocked door.
To overcome the aforementioned concern associated with fluid pressure loss, lock mechanisms have been employed in such rotary door operators.
U.S. Pat. No. 5,545,149 to Jentsch teaches a lock mechanism for lift-and lock door operator type. Such lock mechanism employs a support member positioned under a disk that is permanently attached to the output shaft and an unlocking member which engages such support to prevent its rotation in the unlocking direction. In the door locked position, the disk rests on the support member thus preventing downward movement of the output shaft. The support member incorporates adjustment means to maintain a contact with the disk. The unlocking member is connected to a unlock cylinder. To unlock the door in a normal operation, the unlock cylinder is energized causing rotation of the unlocking member which enables the support member to rotate in the unlocking direction and, more particularly, enables the output shaft to move downwardly and disengage the door wedges.
There are several disadvantages related to this type of lock mechanism. In the first aspect, the disk rests on the support member creating a frictional force that must be overcome during door unlocking movement. In the second aspect, the engagement between support member and the unlocking member, as best understood, creates an additional frictional force. As it is well known in the art, presense of frictional forces causes premature wear and reduces reliability of the design.
U.S. Pat. No. 4,854,223 to Fink teaches a lock mechanism for zero-lead rotary door operator. Such lock mechanism utilizes a blocking lever preventing movement of the roller pair only when fluid pressure loss occurs. The blocking lever is connected to the spring loaded rod of the lock cylinder. In normal operation, the lock cylinder is charged at all times to maintain the blocking lever in the unlock position additionally compressing its internally mounted spring.
There are several disadvantages related to this type of lock mechanism. In the first aspect, if the fluid pressure loss occurs only in regards to the piston-power cylinder unit and not to the lock cylinder, the door will unlock as the blocking lever is maintained in the normal unlock position. In the second aspect, the blocking in the fluid pressure line leading to the lock cylinder may cause late movement of the blocking lever enabling the roller pair to move downwardly and further enabling unlocking of the doors.
As it can be seen from the above discussion there is a need for a relatively simple and reliable mechanical lock mechanism for the rotary door operator.